Obesity is a medical condition which involves the accumulation of excess body fat. It is defined by body mass index (BMI), which is a measure of body weight based upon an individual's weight and height. (BMI=mass(kg)/(height(m))2). Obesity is defined, by both the World Health Organization and the National Institutes of Health, as a BMI greater than or equal to 30, and pre-obesity is defined as a BMI in the 25 to 30 range. Obesity is one of the leading preventable causes of death worldwide, and is thought to reduce life expectancy by around 7 years. Excess body fat in itself can also cause significant perceived issues with cosmesis in healthy individuals.
Many different techniques have been employed to assist individuals who are overweight to lose weight. These include multiple different types of diet, exercise regimes, weight loss medications and weight loss surgery. There is currently no easy or universally effective weight loss solution.
Osteoporosis is a disease of bones that is characterized by a reduction in bone mineral density (BMD), with the result that there is an increased risk of fracture. The World Health Organization defines osteoporosis as a BMD that is 2.5 standard deviations or more below the mean peak bone mass (average of young, healthy adults) as measured by dual energy X-Ray absorptiometry. The development of osteoporosis is determined by the interplay of three factors: first, an individual's peak BMD; second the rate of bone resorption; third, the rate of formation of new bone during remodelling. It is a particular health concern with aging populations in the developed world, especially in post-menopausal women. A variety of pharmacological treatments have been employed to treat osteoporosis with the mainstay of current management being bisphosphonates, which alter the rate that bone is resorbed.
Centrifugation can in effect mimic a gravitational field greater than that experienced on the surface of the Earth (1G), referred to as “hypergravity” (Smith, 1992). It has been observed that chronic centrifugation of animals leads to an alteration of body mass composition (Fuller et al., 2000; Fuller et al., 2002). In particular, animals subjected to hypergravity via centrifugation exhibit a shift in “the proportional distribution of body mass between fat and fat-free components” (Fuller et al., 2000), with a reduction in body fat that is proportional to field strength (Fuller et al., 2002).
Hypergravity has been reported to specifically bring about a reduction in the body fat of chickens (Evans et al., 1969; Smith & Kelly, 1963; Smith & Kelly, 1965; Burton & Smith, 1996), hamsters (Briney & Wunder, 1962), other domestic fowl (Smith et al., 1975), rabbits (Katovich & Smith, 1978), mice (Oyama & Platt, 1967; Keil, 1969; Fuller et al., 2000; Fuller et al., 2002) and rats (Oyama & Platt, 1967; Oyama & Zeitman, 1967; Pitts et al., 1972; Roy et al., 1996; Warren et al., 1998). The observed decrease in body fat can be quite significant. For example, it has been reported that chickens will decrease from 30% body fat at 1G to 3% at 3G (Burton & Smith, 1996). Similarly, mice living at 2G showed approximately a 55% reduction in absolute and percentage carcass fat (Fuller et al., 2000). This seems to be accompanied by an increased usage of fatty acids as a metabolic substrate, and an increased metabolic rate (Fuller et al., 2006).
While marked loss of fat appears to be the principal change in body mass composition to hypergravity, and with it an increase in the relative size of the body's fat-free component, specific changes to the muscles and bones of animals subjected to chronic centrifugation have also been noted by some authors. Small laboratory animals adapted to a 2G environment have been reported to increase their skeletal mass (as measured using body calcium content) by around 18% (Smith, 1992). Jaekel et al. (1977) also reported that prolonged centrifugation at 2.76G led to an increased bone mineral density in rat thigh bones.
The balance between flexor and extensor muscles has been observed to shift in response to hypergravity to favor muscles with an anti-gravity function (Smith, 1992). In domestic fowl on Earth the leg extensor:flexor muscle mass ratio is 0.85 but 2G altered this ratio to 1.17 (Burton & Smith, 1967; Smith, 1992). There also appears to be a functional difference in the muscles of animals exposed to hypergravity. Animals adapted to 2.5G have been reported to demonstrate a markedly increased exercise capacity (as measured by running to exhaustion), of about three-fold that of non-adapted controls, and an increased maximum oxygen uptake (Burton and Smith, 1967, 1996). Hamsters exposed to a 4G environment for 4 weeks were similarly found to have a greater resistance to fatigue in the gastrocnemius muscle and a 37% increase in the strength of its tetanic contraction (Canonica, 1966).
Functional adaptations in the muscles of rats adapted to hypergravity have been examined by analysis of the protein called myosin heavy chain (MHC) (Fuller et al., 2006). Adult rats exposed to 2G for eight weeks were found to have altered MHC characteristics in their soleus and plantaris muscles (Fuller, 2006). Soleus tends to have more slow-twitch fibers, which are better at endurance activities, and plantaris has relatively more fast-twitch fibers, which are better for sprinting but tend to fatigue more rapidly (Gollnick et al., 1974; Fuller et al., 2006). Fuller et al. (2006) found that the rats adapted to 2G had an increase in the slow twitch form of MHC (MHC1) in their soleus muscles, and a converse increase in the fast twitch form of MHC (MHC2b) in their plantaris muscles.
Several mechanisms have been proposed to explain these physiological changes, either alone or in conjunction, including: alterations in mitochondrial uncoupling proteins; fluid volume shifts; alterations in intracranial pressure; increased loading of skeletal muscles; altered feeding behavior; and activation of the vestibular system (Fuller et al., 2000; Fuller et al., 2002). The vestibular system, which is a major contributor to our sense of balance and spatial orientation, consists in each inner ear of three semicircular canals (which detect rotational movement) and the two otolith organs, termed the utricle and saccule, which detect linear acceleration and gravity (Khan & Chang, 2013). They are called otolith organs as they are fluid filled sacs containing numerous free moving calcium carbonate crystals—called otoliths—which move under the influence of gravity or linear acceleration to act upon receptor cells to alter vestibular afferent nerve activity.
Experiments using mutant mice have suggested that the otolith organs are of particular importance in producing the physiological changes observed in animals subjected to chronic centrifugation. In the first experiment, wildtype mice and a type of mutant mice that lack otolith organs but have intact semicircular canals were subjected to 8 weeks of chronic centrifugation at 2G (Fuller et al., 2002). At the end of this period the percentage body fat was significantly reduced in the wildtype mice living at 2G compared to a control population living at 1G (8.5% cf 15.5%), and the percentage lean muscle mass was significantly increased compared to the control population (91.5% cf 83.1%). However, the mutant mice (lacking otolith organs) living at 2G showed no significant change in their body mass composition compared to mutant mice living at 1G.
The second study involved subjecting wildtype and mutant mice (without otolith organs) to just two hours of centrifugation at 2G (Fuller et al., 2004). In the wildtype mice, the authors reported widespread activation (as determined by c-fos upregulation) of a variety of brain structures known to be important in homeostasis and autonomic nervous system regulation including: the dorsomedial hypothalamus (a brain area thought to be of major importance in overseeing feeding behavior and in fixing a set point for body mass (Fuller et al., 2004)); the parabrachial nucleus; the bed nucleus of the stria terminalis; the amygdala; the dorsal raphe; and the locus ceruleus. These findings were not observed in the mutant mice.
The vestibular nuclei (which are located in the pons and medulla and receive input via the vestibular nerve from the vestibular system) are thought to project (both directly and indirectly via the parieto-insular vestibular cortex (PIVC)) to the brainstem homeostatic sites of the parabrachial nucleus (PB) and the peri-aqueductal gray (PAG) (see Chapter 1 and Chapter 3, Section 8 in doctoral thesis by McGeoch, 2010). The PB seems to act to maintain homeostasis—i.e., a stable internal physiological milieu—by integrating this vestibular input with sympathetic input (via lamina 1 spino- and trigemino-thalamic tract fibers) and parasympathetic input (via the nucleus of the solitary tract) (Balaban and Yates, 2004; Craig, 2007; Craig, 2009; McGeoch et al., 2008, 2009; McGeoch, 2010).
It is thought that the PB then acts to maintain homeostasis by means of behavioral, neuroendocrine, and autonomic nervous system efferent (i.e., both sympathetic and parasympathetic) responses (Balaban and Yates, 2004; McGeoch, 2010). Anatomically the PB projects to the insula and anterior cingulate, amygdala and hypothalamus. The insula and anterior cingulate are areas of cerebral cortex implicated in emotional affect and motivation, and hence behavior (Craig, 2009). The hypothalamus plays a vital role in coordinating the neuroendocrine system and, particularly via its dorsomedial aspect, oversees feeding behavior and fixes a set point for body mass composition (Balaban and Yates, 2004; Fuller et al., 2004; Craig, 2007). The amygdala (together again with the hypothalamus and insula) is similarly known to be important in autonomic nervous system control. The PB also outputs to the PAG and basal forebrain, which are also involved in homeostasis (Balaban and Yates, 2004).
The vestibular system is also known to input to the rostral ventro-lateral medulla (RVLM), which is a major sympathetic control site, and it seems likely that any observed modulatory effect of vestibular stimulation on sympathetic function will, at least in part, be mediated via the RVLM (Bent et al., 2006; Grewal et al., 2009; James & Macefield 2010; James et al., 2010; Hammam et al., 2011). However, as the semicircular canals are not involved in modulating sympathetic outflow during vestibular stimulation (Ray et al., 1998), any sympathetic modulation arising from vestibular stimulation must be attributable to activation of the otolith organs (i.e., the utricle and saccule). It is known that white adipose tissue, which constitutes the vast majority of adipose tissue in the human body, is innervated by the sympathetic nervous system and that this innervation regulates the mass of the adipose tissue and the number of fat cells within it (Bowers et al., 2004).
The sympathetic nervous system is also known to innervate mature long bones and by this means plays a modulatory role in bone remodelling (Denise et al., 2006). Bilateral vestibular lesions in rats lead to a decrease in the mineral density of weight bearing bones (Denise et al., 2006). However, this reduction is prevented by the adrenoceptor antagonist propranolol (Denise et al., 2006), which suggests a direct interaction between the vestibular inputs and the sympathetic nervous system. Hence, it appears that the reported increase in bone mineral density in response to hypergravity (Jaekel et al., 1977; Smith, 1992), may also be mediated by a vestibulo-sympathetic effect.
There are also data showing direct pathways connecting the vestibular nuclei with the dorsomedial hypothalamus (Cavdar et al., 2001), which is the part of the hypothalamus already mentioned as being specifically involved in regulating feeding behavior and setting a fixed point for body mass (Fuller et al., 2004).
The hormone leptin is secreted by fat cells and acts upon the hypothalamus to regulate food intake and energy expenditure. Leptin acts to suppress food intake and increase energy expenditure (Hwa et al., 1997), and as such plays a role in regulating body weight. Notably, vestibular stimulation has been found to cause an increase in leptin release (Sobhani, 2002; Sailesh & Mukkadan, 2014).
A chemical approach to vestibular stimulation may be based on betahistine, a partial histamine-3 (H3) receptor antagonist that has been used for some time to treat Meniere's disease. It is also known that by blocking presynaptic H3 receptors, betahistine causes an increased release of histamine and activation of H1 receptors, which is the opposite action to antihistaminic vestibular suppressants (Barak et al., 2008; Baloh & Kerber, 2011). Some early reports have suggested that, at least in certain subgroups, betahistine may be an effective weight loss medication (Barak et al., 2008). Conversely vestibular suppressant medications often lead to weight gain.
Various techniques have been used for research and clinical purposes to stimulate some or all of the components of the vestibular system in humans (Carter and Ray, 2007). These include: (1) Caloric vestibular stimulation, which involves irrigating the outer canal of the ear with warm or cold water or air and mainly stimulates the lateral semicircular canal of that ear; (2) Yaw head rotations, which activates both lateral semicircular canals; (3) Head-down rotation to activate otolith organs and also, initially, semicircular canals; (4) Linear acceleration, which activates otolith organs; (5) Off-vertical axis rotation (OVAR), which activates otolith organs; (6) Galvanic vestibular stimulation (“GVS”), which activates all five components of the vestibular apparatus simultaneously using an electrical current (Fitzpatrick & Day, 2004; St. George & Fitzpatrick, 2011); (7) Click induced vestibular stimulation using an auditory click (Watson & Colebatch, 1998); and (8) Neck muscle vibration induced vestibular stimulation (Karnath et al., 2002). Of these techniques, only one offers the practical option of being produced commercially for home use without expert supervision—GVS.
GVS involves stimulating the vestibular system through the transcutaneous application of a small electric current (usually between 0.1 to 3 milliamps (mA)) via two electrodes. The electrodes can be applied to a variety of locations around the head, but typically one is applied to the skin over each mastoid process, i.e., behind each ear. Some authors term this a “binaural application.” If a cathode and an anode are used with one placed over each mastoid, which is the most common iteration, then this is termed a bipolar binaural application of GVS. The current can be delivered in a variety of ways, including a constant state, in square waves, a sinusoidal (alternating current) pattern and as a pulse train (Petersen et al., 1994; Carter & Ray, 2007; Fitzpatrick & Day, 2004; St. George & Fitzpatrick, 2011).
An electronic appetite suppressant device known as the FOOD WATCHER™ was available on the market in the United Kingdom until recently. The premise behind the FOOD WATCHER™ was that it would act to electrically activate acupuncture points on the ears, with the consequence that a user's appetite would be suppressed. Additionally it was argued that it may suppress appetite by activating the vagus nerve (Esposito et al., 2012).
The FOOD WATCHER™ electrodes were conically shaped plugs designed to be inserted into the external auditory canals (Esposito et al., 2012). The FOOD WATCHER™ is reported to have generated a “signal with amplitude of 40V, frequency of 50 Hz and current of 40 mA through the ear plugs” (Esposito et al., 2012).
A study was carried out on 40 overweight and obese healthy volunteers to investigate the effectiveness of the FOOD WATCHER™ (Esposito et al., 2012). Ten volunteers received the FOOD WATCHER™ and a hypocaloric diet, ten received a hypocaloric diet alone, ten received the FOOD WATCHER™ and a high-protein diet, and ten a high protein diet alone. The authors found that “after 2 months of simultaneous treatment with electric stimulation and diet there was an average weight loss of 7.07 kg in the hypocaloric group and 9.48 kg in the high-protein group, whereas an average weight loss of 5.9 kg and 7.17 kg were observed with hypocaloric and high-protein diet alone, respectively”, leading the authors to conclude that electrical stimulation through the ears may help with weight loss, particularly when used with a high-protein diet, possibly acting via a Yin-yang acupuncture energy balance.
Muscle sympathetic nerve activity (MSNA) to the blood vessels in skeletal muscle can be measured directly in man using microelectrodes. It has been reported that GVS delivered as square wave pulses (at 2 mA of 1 second duration) was ineffective at altering MSNA (Bolton et al., 2004; Carter & Ray, 2007). Conversely, delivering GVS (with an electrode over each mastoid) more dynamically is effective at modulating MSNA. This has been shown using both pulse trains (specifically 10, 1 ms pulses across 30 ms and time-locked to the R wave of the electrocardiogram) (Voustianiouk et al., 2005), and sinusoidal GVS (−2 to 2 mA, 60-100 cycles, applied at administered bipolar binaural GVS (±2 mA, 200 cycles) at frequencies of 0.2, 0.5, 0.8, 1.1, 1.4, 1.7 & 2.0 Hz, to 11 human volunteers while measuring their MSNA (Grewal et al., 2009).
Grewal et al. found a degree of cyclic modulation of MSNA at all frequencies, however, vestibular modulation of MSNA was significantly stronger at 0.2 Hz and significantly weaker at 0.8 Hz. This suggested “that low-frequency changes in vestibular input, such as those associated with postural changes, preferentially modulate MSNA.” Conversely, it was proposed that vestibular inputs around the frequency of the heart rate (i.e., 0.8 Hz, which is 48 beats per minute) compete with, and are inhibited by, the modulation of the MSNA by baroreceptors (pressure detecting mechanoreceptors in the walls of blood vessels), which are activated at the frequency of the heart rate.
The baroreceptor reflex is believed to act via the parasympathetic nervous system (including the vagus nerve and nucleus of the solitary tract) to inhibit the action of the RVLM. This inhibition may be mediated, at least in part, via the caudal ventrolateral medulla (Sved et al., 2000).
Additional evidence to support the argument that vestibular inputs with a frequency distinct from the cardiac frequency are more potent at modulating MSNA, is found in a study in which 8 human subjects were given sinusoidal GVS at their own cardiac frequency, and at ±0.1, ±0.2, ±0.3, ±0.6 Hz from this frequency (James & Macefield, 2010). The authors report that the modulatory effect of the GVS on MSNA activity was impaired when its frequency was closer to the cardiac frequency.
The same authors also measured skin sympathetic nerve activity (SSNA), using microelectrodes, in 11 volunteers subjected to bipolar binaural GVS over the mastoid processes (±2 mA, 200 cycles) at 0.2, 0.5, 0.8, 1.1, 1.4, 1.7 and 2.0 Hz (James et al., 2010). Marked entrainment of GVS was found at all frequencies, although it was significantly weaker at 2.0 Hz. In contrast to the pattern observed with vestibular modulation of MSNA (Grewal et al., 2009), it was reported that the pulse related modulation of SSNA was greater at 0.8 Hz than at 0.2 Hz.
In a recent study, this group found that low frequency sinusoidal GVS (at 0.08, 0.13 and 0.18 Hz) caused two peaks of MSNA modulation (Hammam et al., 2011). This suggested that the primary peak occurs from the positive peak of the sinusoid in which the right vestibular nerve is hyperpolarized and the left depolarized, with the secondary peak of MSNA modulation occurring during the reverse scenario. This behavior was not observed at higher frequencies, possibly because there was insufficient time for a secondary peak to be produced. The authors suggest that this finding indicates “convergence of bilateral inputs from vestibular nuclei onto the output nuclei from which MSNA originates, the rostral ventro-lateral medulla.”
Various uses for vestibular stimulation have been described in related art, including: treating motion sickness (U.S. Pat. No. 4,558,703 to Mark); headsets for stimulation in a virtual environmental (U.S. Pat. No. 6,077,237 to Campbell, et al.); counteracting postural sway (U.S. Pat. No. 6,219,578 to Collins, et al.); to induce sleep, control respiratory function, open a patient's airway and/or counteract vertigo (U.S. Pat. No. 6,748,275 to Lattner, et al.); an in-ear caloric vestibular stimulation apparatus (U.S. Pat. No. 8,262,717 to Rogers, et al.); and to alleviate anxiety (U.S. Pat. No. 8,041,429 to Kirby).
Patent applications have been filed for the following: a method of delivering caloric vestibular stimulation (US Patent Publication 2011/0313498 to Rogers, et al.) and a system and method for reducing snoring and/or sleep apnea in a sleeping person, which may involve the use of GVS (US Patent Publication 2008/0308112 to Bensoussan). Chan, et al. have filed several patent applications for a variety of uses of GVS including: an adaptive system and method for altering the motion of a person (US Patent Publication 2010/0114256); a system for altering motional responses to sensory input (US Patent Publication 2010/0114255); a system and method for providing therapy by altering the motion of a person (US Patent Publication 2010/0114188); a system and method for providing feedback control in a vestibular stimulation system (US Patent Publication 2010/0114187); a system for altering the motional response to music (US Patent Publication 2010/011418); a system and method for game playing using vestibular stimulation (US Patent Publication 2010/0113150); a system and method of altering the motions of a user to meet an objective (US Patent Publication 2010/0112535); and a system and method of training to perform specified motions by providing motional feedback (US Patent Publication 2010/0112533).
GVS is also known to stimulate all components of the vestibular apparatus, including the two otolith organs, and dynamic forms of GVS (i.e., pulse train and sinusoidal) appear to be effective at modulating sympathetic activity. If bipolar binaural sinusoidal GVS is used, the modulation of MSNA is greater when it is administered at a frequency distinct from the cardiac frequency.
In spite of the many reported uses of GVS in the prior art, there has been no teaching or suggestion to apply GVS to alteration of body mass composition in humans. The present invention is directed to such an application.